Formation testers are used to determine properties of earth formations penetrated by wellbores. Typically, a probe is extended outward from a formation tester in a wellbore, so that the probe contacts and seals against a formation.
Unfortunately, insufficient force may be applied to the probe to obtain a seal against the formation (e.g., where the formation is relatively hard), or excessive force may be applied to the probe, thereby damaging the formation (e.g., where the formation is relatively soft). Therefore, it will be readily appreciated that improvements are continually needed in the art of constructing formation testers.